In a paper entitled "Image matching by means of intensity and texture matching in the Fourier domain" by H. S. Stone and C. S. Li that has been presented at the Conference in Image and Video Databases in San Jose, Calif. has been accepted in publication in the Proc. SPIE in January 1996, there is described a process for searching image data bases for images that match a specified pattern. The process has two thresholds that allow the user to adjust independently the closeness of the match. One threshold controls the closeness of the intensity match and the other controls the closeness of the texture match. The thresholds are correlations that can be computed efficiently in the Fourier transform domain of an image, and are especially efficient when the Fourier coefficients are mostly zero. This is especially important when used in conjunction with image-compression schemes that compress by setting small Fourier coefficients to zero.
However, the usefulness of this process is limited because in many practical cases of matching at least one of the images being matched is characterized by occlusions, defined as one or more sub-regions of the images at hand that are irrelevant to the computation of the correlation. Occlusions can arise from external noise (such as sensor noise) malfunction, or drop-outs in the data stream corresponding to the images, or transitory foreign objects in the visual or auditory scene under analysis. Occlusions cause (at times severe) distortion in correlation computations. This distortion arises from the evaluation of the correlation operation over all points in the data set, including the occlusions points. There is a need for a method that effectively removes the distortions caused by occlusions in the computation of the correlation by masking out the occluded points in both data sets being compared so that the correlation computation can be computed only at those points that are not occluded.
The present invention represents an improvement in the process described by essentially eliminating the effect of occlusions in the correlation operation.